1. Field of the Invention
The present invention relates to a positive resist composition suitable for use in the ultramicrolithography process such as production of VLSI or a high-capacity microchip or in other photofabrication processes. More specifically, the present invention relates to a positive photoresist capable of forming a high-resolution pattern by using an electron beam, EUV or the like, that is, a positive resist composition suitably usable for microprocessing of a semiconductor device, where an electron beam or EUV light is used, and a pattern forming method using the composition.
2. Description of the Related Art
In the process of producing a semiconductor device such as IC and LSI, microprocessing by lithography using a photoresist composition has been conventionally performed. Recently, the integration degree of an integrated circuit is becoming higher and formation of an ultrafine pattern in the sub-micron or quarter-micron region is required. To cope with this requirement, the exposure wavelength also tends to become shorter, for example, from g line to i line or further to KrF excimer laser light. At present, other than the excimer laser light, development of lithography using an electron beam, an X ray or EUV light is proceeding.
The lithography using an electron beam or EUV light is positioned as a next-generation or next-next-generation pattern formation technique and a high-sensitivity positive resist is being demanded.
Particularly, in order to shorten the wafer processing time, the elevation of sensitivity is very important. A chemical amplification positive resist generally comprises a resin alkali-insolubilized by protecting an alkali-soluble group with an acid-decomposable group, a photo-acid generator and a basic compound. The photo-acid generator is decomposed upon exposure to generate an acid, the acid decomposes the acid-decomposable group while diffusing in the resist film, and the resin is thereby alkali-solubilized. Accordingly, as the acid generated is a stronger acid, the deprotection reaction is accelerated and higher sensitivity is brought about. However, as the acid generated is a stronger acid, the effect with aging by the acid generated is larger and the storage stability tends to be worsened. Accordingly, it is a very important problem to satisfy both high sensitivity and storage stability. Also, suppression of fluctuation of the pattern line width due to variation in the exposure amount, that is, wide exposure latitude (EL), is demanded.
JP-A-2006-78760 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”) discloses a resist composition having good sensitivity in a lithography process using EUV or an electron beam, where the resist composition comprises an onium salt containing an anion having a structure of N—(—SO2—)2, and JP-A-2007-264051 discloses a positive radiation-sensitive resin composition capable of stably forming a high-precision micropattern, where the positive radiation-sensitive resin composition comprises an onium salt containing an anion having a structure of N—(—SO2—)2 or C—(—SO2—)3.